There may be sudden severe sensori-neural hearing loss to the man having no previous otological symptoms during exposure to the same intensive noise for long time. Till now there were same opinions and theories for the causes of this disease but they are not definitive. The character of this disease is abrupt severe unilateral ""U"" or flat type deafness and positive recruitment phenomenon with tinnitus but no vestibular symptom, and treatment is very difficult. Author experienced three cases of so-called noise-induced sudden deafness. Case I was 35 year male who was employed as compressor driver for 4 years without certain otological symptoms previously. In June of 1980, abrupt left hearing disturbance and tinnitus occurred during work and was treated at local clinic intermittently without improvement, so visited our hospital about 4 months later. Right hearing was mild sensorineural deafness with C⁵ dip and left was moderate-severe flat type. SISI was positive and Bekesy audiogram was Jerger type II on both. There was no improvement in spite of medication of vasodilator and steroid. Case II was 41 year shipman employing in the stokehold for 10 years. He had sudden left hearing loss and tinnitus after work from one week prior of visiting to our hospital. Right audiogram was abrupt descending and left was flat type of moderate-severe hearing loss. SISI was positive on both and Bekesy audiogram was Jerger type I on rignt and type II on left. His symptoms improved with absolute bed rest, lower molecular dextran and vasodilator for 2 months. Case III was a painter of 28 year male who worked in a small tank with intensive noise for 4 months and visited our hospital having complaints of abrupt left hearing loss and tinnitus which occurred 5 days prior of visiting. Right audiogram was high tone deafness and left was flat type of moderate-severe hearing loss. SISI was positive on left and left Bekesy audiogran was Jerger type II. Somewhat improvement was seen with lower molecular dextran, steroid, vasodilator and vitamins for one week.